The semiconductor and related industries, such as the manufacturers of flat panel displays, must handle the semiconductor wafers or substrates which are to become the final product through many processing operations. While the industry has been able to obtain automatic and robotic systems required to meet its substrate handling needs, it has been able to do so only at high cost and with ever increasing complexity. Additionally, as the substrates become larger in order to provide greater economies of scale in the production process, the equipment has become ever larger. As the production equipment has grown in size the need to provide large ultra-clean manufacturing environments has also increased, which are quite costly. These factors have combined in creating a very significant increase in semiconductor manufacturing costs, which costs are ultimately passed on to the customer, and hence the risks involved in building new production facilities in these substrate processing industries also increase.
A major difficulty in reducing the complexity and the size of the systems heretofore available has been that the wafer handling mechanisms previously provided all have essentially moved the wafer or substrate from process to process sequentially in the horizontal plane. While one or two of process stations may, in some cases, have been disposed in a vertical arrangement in order to reduce the "footprint" of the apparatus, the substantial portion of the wafer handling is still done in the horizontal plane. Furthermore, when the handling architecture of a system is in the horizontal plane the use of a simplified handling means has not been feasible. For this reason, complex robotic "random access" handling means have been employed to move the wafers individually among the process stations.
Still another shortcoming of the prior art handling devices is that most handling systems move one or at most two wafers at a time. The central or even multiple central handling systems cannot by their nature be in two places at once but are constrained to address only one or at most two wafer handling occurrences at a time. In the case of two wafer handling occurrences, wafer handling typically does not occur simultaneously but rather in close time proximity. Therefore, these prior wafer handling techniques have had the effect of increasing the time that the system spends handling the wafers and decreasing the time available for a process system to process the wafers. This is often referred to as handling "overhead" and the greater the handling "overhead", the less productive the system.
Accordingly, it is an object of present invention to provide a wafer handling system which obviates the disadvantages of the prior handling systems, and which is more compact in size enabling a reduction in facilities cost, far simpler enabling an increase in system operational reliability while reducing system cost, and which reduces handling "overhead" time thereby increasing system productivity and throughput.
The foregoing objects, features and various advantages of the present invention will be more readily apparent from the following detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.